Forwarding data between an array of baseband units and an array of radio heads in distributed wireless system using TDM switches

ABSTRACT

The present disclosure discloses a distributed system. The distributed system includes a plurality of radio heads and a plurality of controllers disposed in one or more chassis external to the plurality of radio heads. Each of the plurality of controllers includes a baseband unit (BBU), an uplink time-division multiplexing (TDM) switch and a downlink TDM switch. The uplink TDM switch and the downlink TDM switch forward data bits between a radio head and a BBU by using TDM cells which may reduce latency relative to using Ethernet frames.

BACKGROUND

Access points (APs) used in Wi-Fi networks include a Media AccessControl (MAC), a baseband unit (BBU), and a Radio Frequency (RF)transceiver. The BBU transmits baseband signals to the radio. The radioconverts the baseband signals to wireless signals and transmits thewireless signals to client devices. Communication between the BBU andthe radio needs very low latency (e.g., less than 10 microseconds) to becompliant with the 802.11 standard.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 shows a distributed system, according to one embodiment herein.

FIG. 2 shows a central controller, according to one embodiment herein.

FIG. 3A shows the transmission of an uplink channel stream, according toone embodiment herein.

FIG. 3B shows the transmission of an uplink channel stream, according toanother embodiment herein.

FIG. 3C shows the transmission of an uplink channel stream, according toanother embodiment herein.

FIG. 4 shows the transmission of a downlink channel stream, according toone embodiment herein.

FIG. 5 shows a time-division multiplexing (TDM) cell, according to oneembodiment herein.

FIG. 6 shows a flowchart chart of a method for switching an uplinkchannel stream, according to one embodiment herein.

FIG. 7 shows a flowchart chart of a method for switching a downlinkchannel stream, according to one embodiment herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

One embodiment of the present disclosure provides a system. The systemincludes a plurality of radio heads, wherein each of the plurality ofradio heads comprises at least one antenna and at least one transceiver.The system also includes a plurality of controllers disposed in one ormore chassis external to the plurality of radio heads. Each of theplurality of controllers comprises: a BBU and an uplink time-divisionmultiplexing (TDM) switch coupled to (i) at least a first radio head ofthe plurality of radio heads, (ii) the BBU in the controller, and (iii)at least one uplink TDM switch in a different controller of theplurality of controllers. The uplink TDM switch is configured to:receive a first TDM cell based on signals received from the first radiohead, wherein the first TDM cell comprises a first plurality of TDM dataslots, and wherein a destination of each of the first plurality of TDMdata slots is predetermined; generate a second TDM cell based on thefirst TDM cell, wherein the second TDM cell comprises a second pluralityof TDM data slots, and wherein a destination of each of the secondplurality of TDM data slots is predetermined; forward data bits in afirst slot of the first plurality of TDM data slots to the BBU in thecontroller; and forward data bits in a second slot of the firstplurality of TDM data slots in the second TDM cell to the at least oneuplink TDM switch in the different controller.

One embodiment of the present disclosure provides integrated circuit.The integrated circuit includes a BBU and an uplink time-divisionmultiplexing (TDM) switch coupled to (i) at least a first radio head,(ii) the BBU in the integrated circuit, and (iii) at least one uplinkTDM switch in a different integrated circuit. The uplink TDM switch isconfigured to: receive a first TDM cell based on signals received fromthe first radio head, wherein the first TDM cell comprises a firstplurality of TDM data slots, and wherein a destination of each of thefirst plurality of TDM data slots is predetermined; generate a secondTDM cell based on the first TDM cell, wherein the second TDM cellcomprises a second plurality of TDM data slots, and wherein adestination of each of the second plurality of TDM data slots ispredetermined; forward data bits in a first slot of the first pluralityof TDM data slots to the BBU in the integrated circuit; and forward databits in a second slot of the first plurality of TDM data slots in thesecond TDM cell to the at least one uplink TDM switch in the differentintegrated circuit.

One embodiment of the present disclosure provides a controller. Thecontroller includes a BBU and a memory containing a program that, whenexecuted on the BBU, performs an operation. The operation comprises:receiving a first TDM cell based on signals received from a first radiohead, wherein the first TDM cell comprises a first plurality of TDM dataslots, and wherein a destination of each of the first plurality of TDMdata slots is predetermined; generating a second TDM cell based on thefirst TDM cell, wherein the second TDM cell comprises a second pluralityof TDM data slots, and wherein a destination of each of the secondplurality of TDM data slots is predetermined; forwarding data bits in afirst slot of the first plurality of TDM data slots to the BBU in thecontroller; and forwarding data bits in a second slot of the firstplurality of TDM data slots in the second TDM cell to at least adifferent controller.

Example Embodiments

In one embodiment, the APs are part of a distributed system. Thedistributed system includes central controllers and radio heads (RHs)that are distributed at different physical locations. The RHs areusually connected to the central controllers through Ethernet links.Transmitting data through Ethernet links between a RH and a centralcontroller using Ethernet frame format (e.g., IEEE 802.3 frame format)and delaying processing for the cyclic redundancy check (CRC)verification may introduce extra latency (e.g., several microseconds)that negatively impacts the client devices and compliance with the802.11 Short Interframe Space (SIFS) and SLOT timing. For a systemincluding distributed RHs, this provides implementation challenges notpresent in more traditional designs. When an array of RHs is connectedto an array of BBUs, a means of forwarding waveforms between antennas ofRHs and the desired BBU with low latency provides additionalimplementation challenges. The present disclosure provides embodimentsfor transmitting data between a RH and a central controller with verylow latency, e.g., less than 9 microseconds.

FIG. 1 illustrates a distributed system 100, according to one embodimentherein. As shown in FIG. 1, the system 100 includes one or more chassis,e.g., the three chassis 101, 102 and 103. Each of the chassis includesone or more central controllers 104. For example, as shown in FIG. 1,the chassis 101 includes three central controllers 104, i.e., thecentral controller A, the central controller B and the centralcontroller C. In one embodiment, multiple central controllers 104 areinstalled as a rack system in one chassis. In one embodiment, thecentral controllers 104 in one chassis are application-specificintegrated circuits (ASICs) placed on a printed circuit board (PCB). Inone embodiment, the central controllers 104 in one chassis are ASICs ondifferent line cards. In one embodiment, the central controllers 104 canbe firmware or combinations of software and hardware. For example, eachof the central controllers 104 may include one or more processors andone or more memories containing one or more programs executed by theprocessor(s). In one embodiment, the central controllers 104 may includeone or more processing units with physical borders.

In one embodiment, each of the central controllers 104 directly connectswith one or more RHs 111. As shown in FIG. 1, the central controller Ghas connections with two RHs 111, i.e., the RH A and the RH B. In oneembodiment, each of the RHs 111 includes one or more antennas tocommunicate radio frequency (RF) wireless signals with one or moreclient devices. In FIG. 1, the RH A includes two antennas 112 and 113 tocommunicate RF signals with the client device 116. In one embodiment,the RHs are physical connected to the central controller through wiredconnections, e.g., Cat5e/6/6a Ethernet cables such as using10GBASE-T/NBASE-T. In another embodiment they are connected throughfiber-optic links using 10GBASE-SR/10GBASE-LR. The RH A and the RH B arephysically connected to the central controller G through two Ethernetlinks 114 and 115, respectively. In one embodiment, the RHs aredistributed at different geographic locations in an area, e.g., abuilding. For example, the RH A and the RH B may be located on twodifferent floors in a building but are physically connected to the samecentral controller G.

In one embodiment, in the distributed system 100, functions of an AP aresplit into two parts. Each of the central controllers 104, e.g., thecentral controller G, provides part or all of the digital part of thephysical (PHY) layer function for baseband processing (e.g., channelcoding) and the media access control (MAC) layer function (e.g.,collision avoidance) of an AP. In one embodiment, each of the centralcontrollers 104 includes one or more BBUs for baseband processing. EachRH 111, e.g., the RH A, provides the analog part of the PHY layerfunction for transmitting and receiving RF signals in a frequency band,plus associated digital signal processing (e.g., up-sampling and Q-to-Icalibration). For example, each RH 111 may include one or more radiotransceivers.

In one embodiment, the central controllers 104 do not perform the analogpart of the PHY layer function of an AP, i.e., only the RHs 111 includeand perform the analog part of the PHY layer function of an AP, e.g.,transmitting and receiving RF signals in a frequency band. In oneembodiment, the RHs 111 do not perform the digital part of the PHY layerfunction and the MAC layer function of an AP, i.e., only the centralcontrollers 104 include and perform the digital part of the PHY layerfunction and the MAC layer function of an AP. In one embodiment, part orall of the digital part of the PHY layer function may also be includedin the RHs depending on system partitioning.

In one embodiment, the central controllers 104 are physically connectedwith each other so that the central controllers 104 can transmit databetween each other. In one embodiment, the central controllers 104 thatare in the same chassis are physically connected with each other to forma ring. For example, the central controllers A, B and C are in the samechassis 101 and are physically connected with each other to form a ringA. Similarly, the central controllers D, E and F in the chassis 102 arephysically connected with each other to form a ring B, and the centralcontrollers G, H and I in the chassis 103 are physically connected witheach other to form a ring C.

In another embodiment, the central controllers 104 that are in differentchassis are physically connected with each other for form a stack. Forexample, the central controllers A, D and G (which are all in differentchassis) are physically connected with each other to form a stack A.Similarly, the central controllers B, E and H are physically connectedwith each other to form a stack B, and the central controllers C, F andI are physically connected with each other to form a stack C. That is, astack connects multiple central controllers 104 that are each indifferent chassis. Having more than one stack, providing more than oneforwarding path between two controllers not directly connected can beused to increase the available bandwidth, or provide paths with fewerhops over links and/or TDM switches in order to reduce latency.

In one embodiment, the central controllers 104 are physically connectedwith each other through wired connections. For example, as shown in FIG.1, the central controllers A, B and C in the same chassis 101 arephysically connected with each other using Ethernet links, high speedSerializer/Deserializer (SerDes), or other I/O interfaces to form thering A. In one embodiment, the central controllers A and C are connectedthrough at least one Ethernet link 121, the central controllers A and Bare connected through Ethernet link 122, and the central controllers Band C are connected through Ethernet link 123. The central controllers104 in ring B and ring C are connected by using Ethernet links in asimilar way. In one embodiment, the Ethernet links connecting thecentral controllers in the same chassis are full duplex that cantransmit data in two directions, e.g., from the central controller A tothe central controller C and vice versa.

Similarly, the central controllers A, D and G in different chassis arephysically connected with each other using Ethernet links to form thestack A. For example, the central controllers A and G are connectedthrough at least one Ethernet link 131, the central controllers A and Dare connected through at least one Ethernet link 132, and the centralcontrollers D and G are connected through at least one Ethernet link133. The central controllers 104 in stack B and stack C are connectedusing Ethernet links in a similar way. In one embodiment, the Ethernetlinks connecting the central controllers in the same stack are fullduplex that can transmit data in two directions, e.g., from the centralcontroller A to the central controller G and vice versa.

FIG. 1 shows only one embodiment. In other embodiments, the distributedsystem 100 can include a different number of chassis. And each chassiscan include a different number of central controllers, which, in turn,can control a different number of RHs. Further, each RH can include adifferent number of antennas. The central controllers can connect witheach other to form the rings and/or the stacks in different ways, asunderstood by an ordinary person in the art. The central controllers canconnect with each other using different topologies. For example, thecentral controllers can connect with each other using a mesh topology ora hub-and-spoke CLOS topology, as understood by an ordinary person inthe art.

In one embodiment, a central controller 104 generates and/or processesthe data for the RHs 111 that are physically connected to it. Forexample, the central controller G generates baseband signals carryingdata for the client devices.

In another embodiment, the central controller that generates and/orprocesses the data for a RH is not the central controller that the RH isphysically connected to. For example, while the RH A is physicallyconnected to the central controller G the signals provided by the RH Acan be processed by the central controller I in the same chassis 103 orby the central controller C in a different chassis 101. That is, thedata from the RH A may not be processed by the central controller G thatis physically connected to the RH A. In another example, the signalsreceived from all nearby RHs operating on the same frequency channelshould be processed by the same central controller, although the nearbyRHs may be physically connected to different central controllers. In oneembodiment, the signals received using some antennas on the RH areprocessed by one central controller while the signals received fromother antennas on the same RH are processed by a different centralcontroller. For example, it is assumed that the antenna 112 on RH Aserves the 2.4 GHz frequency band and the antenna 113 on RH A serves the5 GHz frequency band. The signals received from the antenna 112 may beprocessed by the central controller G and the signals received from theantenna 113 may be processed by the central controller I.

In the present disclosure, a RH can be physically connected to anycentral controller, e.g., the central controller that is associated withthe physical port connecting to the RH, while the data for the RH can beprocessed by a different central controller if desired, e.g., thecentral controller that is processing all the antennas on a specificchannel. This is achieved by using the rings and the stacks shown inFIG. 1 that interconnect the central controllers 104 in the system 100.

FIG. 2 shows a central controller 104, according to one embodimentherein. In FIG. 2, the central controller 104 is the central controllerG in FIG. 1 for explanation purpose. In one embodiment, the othercentral controllers 104 in the distributed system, e.g., the centralcontrollers A and F in FIG. 1, are substantially the same as the centralcontroller 104 shown in FIG. 2.

The central controller G includes a BBU 201 for baseband processing. Inone embodiment, the BBU can be hardware circuits or a mixture offirmware and hardware capable of performing the baseband processing. Thecentral controller G also includes an uplink time-division multiplexingswitch (UL-TDM switch) 202 and a downlink time-division multiplexingswitch (DL-TDM switch) 203. The central controller G further includes arespective I/O interface for each RH physically connected to the centralcontroller G. For example, the central controller G includes I/Ointerface 204 for RH A and I/O interface 205 for RH B. In oneembodiment, the I/O interfaces 204 and 205 can be RJ45 ports, e.g., 10Gbit/s RJ45 ports. In another embodiment they may be Small Form-factorPluggable (SFP) or SFP+ports (or similar) with various modules.

In one embodiment, the RH A is connected to the I/O interface 204through an Ethernet link 114, e.g., a 10GBASE-T link. In one embodiment,the RH A transmits raw waveform data, e.g., uplink digitized analogsignals to the UL-TDM switch 202 through the I/O interface 204. As shownin FIG. 2, the UL-TDM switch 202 transmits the uplink digitized signalsas input TDM cells to a formatting module 212 between the UL-TDM switch202 and the BBU 201. The formatting module 212 formats the input TDMcells into output TDM cells and transmits the output TDM cells to theBBU 201 or to an UL-TDM switch in a different central controller.

In one embodiment, the BBU 201 generates downlink baseband digitalsignals for a client device. The BBU 201 transmits the downlink basebanddigital signals to the DL-TDM switch 203. As shown in FIG. 2, the BBU201 transmits the downlink baseband digital signals to a formattingmodule 213 between the BBU 201 and the DL-TDM switch 203. The formattingmodule 213 formats the downlink baseband digital signals into TDM cellsand transmits the TDM cells to the DL-TDM switch 203 as input TDM cells.The DL-TDM switch 203 places the received input TDM cells incorresponding output TDM cells and forwards the output TDM cells throughthe I/O interface 204 to the RH A 201 or to a DL-TDM switch in adifferent central controller. In one embodiment, each RH, e.g., the RH A201, has a matching module 214 to convert the received TDM cells todigitized downlink analog signals which are transmitted to the clientdevice.

FIG. 2 shows only one embodiment. In other embodiments, the centralcontroller 104 can include multiple BBUs. In other embodiments, thecentral controller 104 can include other components such as memoryelements. In other embodiments, the UL-TDM switch 202 and the DL-TDMswitch 203 communicate data with the BBU 201 through one or moreinternal I/O interfaces. In other embodiments, the UL-TDM switch 202 andthe DL-TDM switch 203 are the same switch or included in the same switchcircuit. In other embodiments, the central controller 104 includesmultiple UL-TDM switches. For example, the central controller 104 mayinclude a first level UL-TDM switch and a second level UL-TDM switch.The RH A transmits uplink digital signals to the first level UL-TDMswitch, which forwards the uplink digital signals to the second levelUL-TDM switch. The second level UL-TDM switch transmits the uplinkdigital signals to the formatting module 212, which transmits TDM cellsto the BBU 201. Similarly, in other embodiments, the central controller104 includes multiple DL-TDM switches.

In the following, the raw waveform data, e.g., uplink or downlinkdigitized analog signals, transmitted between a RH and a BBU in acentral controller is defined as a channel stream. That is, a channelstream is associated with two stream endpoints, i.e., a RH and a BBU ina central controller. An uplink channel stream is transmitted from a RHto a BBU. A downlink channel stream is transmitted from a BBU to a RH.The present disclosure provides embodiments for transmitting channelstreams between a RH and the corresponding BBU (which may be disposed ina central controller that not directly connected to the RH) forprocessing the channel streams with very low latency, e.g., less than 10microseconds. In the following figures, the formatting modules in thecentral controllers and the matching modules in the RHs are omitted forsimplicity of illustration.

FIG. 3A shows the transmission of an uplink channel stream, according toa one embodiment herein. FIG. 3A shows an embodiment to transmit anuplink channel stream from the RH A connected to the central controllerG in the chassis 103 to the BBU 301 of the central controller I in thesame chassis 103. The RH A transmits the uplink channel stream to theUL-TDM switch 202 through the I/O interface 204 in the centralcontroller G by using the Ethernet link 114. The UL-TDM switch 202forwards the uplink channel stream to the UL-TDM switch 302 in thecentral controller I by using the Ethernet link 331. In one embodiment,the Ethernet link 331 is part of the ring C illustrated in FIG. 1. TheUL-TDM switch 302 forwards TDM cells carrying the uplink digital signalsto the BBU 301 in the central controller I through an internalconnection 332. The BBU 301 processes the uplink digital signals for theRH A.

For simplicity of illustration, in FIG. 3A, the central controllers onlyshow the UL-TDM switches and omit the DL-TDM switches. Also, for thecentral controller G, FIG. 3A only shows the RH A connecting to thecentral controller G and the I/O interface 104, and omits the RH B andthe I/O interface 105. Moreover, FIG. 3A only shows the centralcontrollers G and I in the chassis 103, and omits the central controllerH in the chassis 103. In the following FIGS. 3B, 3C and 4, similaromissions are applied for simplicity of illustration.

FIG. 3B shows the transmission of an uplink channel stream, according toa one embodiment herein. FIG. 3B illustrates transmitting an uplinkchannel stream from the RH A connected to the central controller G inthe chassis 103 to the BBU 311 of the central controller A in adifferent chassis 101. The RH A transmits the uplink channel stream tothe UL-TDM switch 202 through the I/O interface 204 in the centralcontroller G by using the Ethernet link 114, similarly to FIG. 3A. TheUL-TDM switch 202 forwards the uplink channel stream to the UL-TDMswitch 312 in the central controller A using the Ethernet link 333. Inone embodiment, the Ethernet link 333 is part of the stack A illustratedin FIG. 1. The UL-TDM switch 312 converts the uplink channel stream touplink digital signals and forwards the uplink digital signals to theBBU 311 in the central controller A through an internal connection 334.The BBU 311 processes the uplink digital signals for the RH A.

FIG. 3C shows the transmission of an uplink channel stream, according toa one embodiment herein. FIG. 3C illustrates transmitting an uplinkchannel stream from the RH A connected to the central controller G inthe chassis 103 to the BBU 321 of the central controller C in adifferent chassis 101. The RH A transmits the uplink channel stream tothe UL-TDM switch 202 through the I/O interface 204 in the centralcontroller G by using the Ethernet link 114, similarly to FIG. 3A orFIG. 3B. The UL-TDM switch 202 forwards the uplink channel stream to theUL-TDM switch 312 in the central controller A by using the Ethernet link333. The UL-TDM switch 312 forwards the uplink channel stream to theUL-TDM switch 322 in the central controller C using the Ethernet link335. In one embodiment, the Ethernet link 335 is part of ring A. TheUL-TDM switch 322 forwards TDM cells carrying the uplink digital signalsto the BBU 321 in the central controller C through an internalconnection 336 which processes the uplink digital signals for the RH A.

In one embodiment, the two stream endpoints associated with an uplinkchannel stream can be changed dynamically due to changes of load and/orRF environment. For example, FIG. 3A shows an embodiment to transmit anuplink channel stream from the RH A to the BBU 301 of the centralcontroller I in the same chassis 103. Due to changes of load and/or RFenvironment, the uplink channel stream may instead be transmitted fromthe RH A to the BBU 311 of the central controller A in the chassis 101for better global optimization of antenna usage. In this case, theUL-TDM switch 202 can forward the uplink channel stream from the RH Aaccording to the change. In one embodiment, an uplink channel streambetween two stream endpoints may be stopped due to changes of loadand/or RF environment. For example the uplink channel stream transmittedfrom the RH A to the BBU 301 of the central controller I may not providethe best usage of limited resources and thus is not used. In this case,the UL-TDM switch 202 does not forward the uplink channel stream fromthe RH A to the BBU 301. In one embodiment, a new uplink channel streamis transmitted between two stream endpoints. For example, a new uplinkchannel stream is created between the RH A to the BBU in the centralcontroller H in the same chassis 103. In this case, the centralcontroller configures the UL-TDM switch to forward the new uplinkchannel stream from the RH A to the BBU in the central controller H. Inanother embodiment, the system 100 can dynamically adjust the forwardingpath between the two stream endpoints in one or more TDM switches toaccommodate new channel streams.

In one embodiment, each UL-TDM switch in the central controllers has arespective I/O interface, e.g., a 10 Gbit/s port, for each linkconnection of the UL-TDM switch to another UL-TDM switch (aninter-switch connection). For example, the UL-TDM switch 202 in thecentral controller G has a first I/O interface to connect to theEthernet link 331 and a second I/O interface to connect to the Ethernetlink 333. In another example, the UL-TDM switch 312 in the centralcontroller A has a first I/O interface to connect to the Ethernet link333 and a second I/O interface to connect to the Ethernet link 335.

In FIGS. 3A and 3B, the uplink channel stream is transmitted between twostream endpoints, i.e., the RH and the BBU processing the uplink channelstream, through only two UL-TDM switches in two central controllers viaonly one ring or only one stack. The transmission in FIG. 3A or 3B isdefined as a one-hop switching, not counting the link between the firstswitch and the RH. In FIG. 3C, the uplink channel stream is transmittedfrom the RH to the BBU processing the uplink channel stream throughthree UL-TDM switches in three central controllers via both a ring and astack. The transmission in FIG. 3C is defined as a two-hop switching.N-hop switching can be defined similarly, where N is zero or a positiveinteger. That is, if the uplink channel stream is transmitted betweentwo stream endpoints through M UL-TDM switches in M central controllers,then N=M−1. In one embodiment, the uplink channel stream is transmittedbetween two stream endpoints using at most a two-hop switching. In otherembodiments, the uplink channel stream is transmitted between two streamendpoints via one or more rings, one or more stacks or a combination ofone or more rings and stacks.

FIG. 4 shows the transmission of a downlink channel stream, according toa one embodiment herein. FIG. 4 illustrates transmitting a downlinkchannel stream from the BBU 321 of the central controller C in chassis101 to the RH A physically connected to the central controller G in thechassis 103. The BBU 321 transmits the downlink baseband digital signalsto the DL-TDM switch 324 through an internal connection 342. The DL-TDMswitch 324 transmits the downlink channel stream (i.e., a stream of TDMcells) to the DL-TDM switch 314 in the central controller A by using theEthernet link 340. The Ethernet link 340 in FIG. 4 is different from theEthernet link 335 in FIG. 3C. In one embodiment, the Ethernet link 340provides a part of the ring A. The DL-TDM switch 314 forwards thedownlink channel stream to the DL-TDM switch 203 in the centralcontroller G by using the Ethernet link 341. The Ethernet link 341 inFIG. 4 is different from the Ethernet link 333 in FIG. 3C. In oneembodiment, the Ethernet link 341 is part of stack A in FIG. 1. TheDL-TDM switch 203 forwards the digitized downlink analog signals throughthe I/O interface 204 to the RH A 201 for transmitting to the clientdevice.

Similarly as described above, in one embodiment, the two streamendpoints associated with a downlink channel stream can be changed dueto changes of load and/or RF environment. In other embodiments, adownlink channel stream may not be used, or a new downlink channelstream may be created. In these embodiments, the DL-TDM switch in eachcentral controller can make adjustments accordingly.

In one embodiment, each DL-TDM switch in the central controllers has arespective I/O interface, e.g., a 10 Gbit/s port, for each linkconnection of the DL-TDM switch to another DL-TDM switch (aninter-switching connection). For example, the DL-TDM switch 314 in thecentral controller A has a first I/O interface to connect to theEthernet link 340 and a second I/O interface to connect to the Ethernetlink 341. In one embodiment, in each central controller, the I/Ointerfaces of the UL-TDM switch for inter-switching connections aredifferent from the I/O interfaces of the DL-TDM switch forinter-switching connections. For example, in the central controller A,the two I/O interfaces of the UL-TDM switch 312 to connect to Ethernetlinks 335 and 333 are different from the two I/O interfaces of theDL-TDM switch 314 to connect to Ethernet links 340 and 341. On the otherhand, in each central controller, the UL-TDM switch and the DL-TDMswitch share the same I/O interface to connect to a RH, as described inFIG. 2 above.

In FIG. 4, the downlink channel stream is transmitted from the BBUgenerating the downlink channel stream to the RH through three DL-TDMswitches in three central controllers via both a ring and a stack. Thatis, similarly as described above, the transmission in FIG. 4 is atwo-hop switching. In one embodiment, the downlink channel stream istransmitted between two stream endpoints using at most a two-hopswitching.

FIGS. 3A-3C and FIG. 4 only show a few embodiments. In otherembodiments, a channel stream can be transmitted between any RH and anyBBU of any central controller in the distributed system 100 similarly asdescribed above. In other embodiments, the channel stream is transmittedbetween two stream endpoints using more than two-hop switching, e.g., athree-hop switching. In other embodiments, the RH itself can include anUL-TDM switch and/or a DL-TDM switch.

In one embodiment, in order to achieve very low latency for transmittingchannel streams between two stream endpoints using Ethernet links, datais transmitted in the channel streams as TDM cells, as described indetail below.

FIG. 5 shows a TDM cell 500, according to one embodiment herein. Asshown in FIG. 5, the TDM cell 500 includes a plurality of data bits thatmay be divided into a plurality of data slots, e.g., two data slots 501and 502. Each data slot includes a plurality of bits, and the number ofdata bits in each data slot need be the same. In one embodiment, eachdata slot in the TDM cell 500 includes a channel stream corresponding totwo stream endpoints in the distributed system 100, i.e., a RH and aBBU. That is, data bits in each data slot are transmitted between twostream endpoints. In the following, the transmission of the TDM cell 500will be explained using one or more of FIGS. 1-4 above.

In one embodiment, each data slot in the TDM cell 500 includes an uplinkchannel stream transmitted from a same RH. For example, the RH Atransmits digitized analog signals to the UL-TDM switch 202 in thecentral controller G that the RH A is physically connected to. TheUL-TDM switch 202 generates one or more TDM cells 500 based on thereceived digitized analog signals from the RH A. Each of the data slotsin a TDM cell 500 corresponds to an uplink data stream. For example,data bits in the data slot 501 are transmitted from the RH A to the BBU201 in the central controller G. Data bits in the data slot 502 aretransmitted from the RH A to the BBU 301 in the central controller I, asshown in FIG. 3A. Thus, after generating the TDM cell 500, the UL-TDMswitch 202 forwards data bits in the data slot 501 to the BBU 201 in thecentral controller G. Also, the UL-TDM switch 202 forwards data bits inthe data slot 502 to the UL-TDM switch 302 in the central controller Ithrough the Ethernet link 331, as shown in FIG. 3A. In one embodiment,each channel stream corresponds to an end to end communication tunnel.In one embodiment, for transmitting multiple channel streams, eachchannel stream includes multiple data slots of varying sizes. In anotherembodiment, a channel stream is fragmented into a plurality of dataslots that are sent over a plurality of I/O interfaces. In anotherembodiment, a channel stream is fragmented into a plurality of dataslots that are sent in the same data slot in different TDM cells, toreduce TDM bandwidth required to forward slower sampling rates.

In another embodiment, each data slot in the TDM cell 500 includes adownlink channel stream generated by a same BBU. For example, the BBU321 in the central controller C generates baseband digital signals andtransmits the baseband digital signals to the DL-TDM switch 324. TheDL-TDM switch 324 generates a TDM cell 500 based on the receivedbaseband digital signals from the BBU 321. Each of the two data slots inthe TDM cell 501 is corresponding to a downlink data stream. Forexample, data bits in the data slot 501 are transmitted from the BBU 321to a RH physically connected to the central controller C. Data bits inthe data slot 502 are transmitted from the BBU 321 to the RH Aphysically connected to the central controller G, as shown in FIG. 4.Thus, after generating the TDM cell 500, the DL-TDM switch 324 forwardsdata bits in the data slot 501 to the RH physically connected to thecentral controller C. Also, the DL-TDM switch 324 forwards data bits inthe data slot 502 to the DL-TDM switch 314 through the Ethernet link340, as shown in FIG. 4.

In one embodiment, the TDM cell 500 includes 124 bits. In oneembodiment, most or all the bits in the TDM cell 500 are contiguous databits. For example, the bits in the TDM cell 500 do not include overheadbits such as the bits indicating one or more source addressestransmitting the data bits, one or more destination addresses receivingthe data bits or the CRC bits. That is, the TDM cell 500 does not haveas many overhead bits as in an Ethernet frame and thus the latency oftransmitting the TDM cell 500 is very low, while allowing each data slotto be forwarded to a different destination. In other words, TDM cells,instead of Ethernet frames, are transmitted between RHs and BBUs byusing Ethernet links in the distributed system 100 to achieve very lowlatency.

In one embodiment, in each central controller, the UL-TDM switch and theDL-TDM switch is pre-configured by the central controllers to know whereto forward the data bits in each data slot of the TDM cell 500. That is,the destination of each data slot 501, 502 is predetermined and known bythe UL-TDM switch and the DL-TDM switch. In one embodiment, the UL-TDMswitch and the DL-TDM switch can determine where to forward the databits based on chronological or bit positions of the data bits or dataslots in each TDM cell. For example, the UL-TDM switch 202 knows thatbits 1-20 (the first data slot 501) in each TDM cell 500 over I/Ointerface 204 should be forwarded to the BBU 201 in the centralcontroller G and bits 21-40 (the second data slot 502) in each TDM cell500 over I/O interface 204 should be forwarded to the UL-TDM switch 302in the central controller I through the Ethernet link 331. Thus, unlikein Ethernet frames, the central controller do not need to process headerto determine the destination of the frame. Instead, which slot the datais located in determines where the data will be forwarded, which reducesthe amount of time required to forward the TDM cell 500 in the channelstreams. This can save both the time in determining the forwardingdecision and the time to transfer the data used in determining theforwarding decision.

In one embodiment, information of the chronological positions indicatingthe destination can be pre-programmed into the UL-TDM switch and theDL-TDM switch. In another embodiment, each UL-TDM switch and each DL-TDMswitch may include a respective predetermined transfer matrix indicatingwhere the data bits are coming from and where the data bits should beforwarded to for each data slot in the TDM cells. In another embodiment,the TDM switch may contain a plurality of transfer matrices, withtimestamps indicating when configuration changes will occur.

In another embodiment, in each central controller, the UL-TDM switch andthe DL-TDM switch knows where to forward the data bits in each data slotof the TDM cell by using signaling bits in the TDM cell 500. Forexample, some bits in the TDM cell 500 can be signaling bits (not databits) including information of the destination of each data slot in theTDM cell 500. The UL-TDM switch and/or the DL-TDM switch receive thesignaling bits in the TDM cell and determine the destination of eachdata slot using the information included in the signaling bits. Thesignaling bits in the TDM cell 500 introduce less overhead than theoverhead bits in an Ethernet frame. For example, the signaling bits inthe TDM cell 500 can be one or two bits while the overhead bits in anEthernet frame are typically several hundred bits.

FIG. 6 shows a flowchart chart of a method 600 for switching an uplinkchannel stream, according to one embodiment herein. At block 601, anUL-TDM switch receives a first TDM cell based on digitized analogsignals received from a first RH coupled to the UL-TDM switch in an IC,wherein the first TDM cell comprises a first plurality of TDM dataslots, and wherein a destination of each of the first plurality of TDMdata slots is predetermined. For example, as described above, the UL-TDMswitch 202 in the central controller G receives a first TDM cell 500based on the received digitized analog signals from the RH A. The firstTDM cell 500 includes data slot 501 and data slot 502 that have knowndestinations. The first TDM cell 500 is input to the UL-TDM switch 202as an input TDM cell. At block 602, the UL-TDM switch generates a secondTDM cell based on the first TDM cell, wherein the second TDM cellcomprises a second plurality of TDM data slots, and wherein adestination of each of the second plurality of TDM data slots ispredetermined. For example, the UL-TDM switch 202 generates a second TDMcell 500 as the corresponding output TDM cell based on the input TDMcell. At block 603, the UL-TDM switch forwards data bits in a first slotof the first plurality of TDM data slots to a BBU in the IC. Forexample, the UL-TDM switch 202 places data bits in the data slot 501 ofthe input TDM cell in the data slot 501 of the output TDM cell andforwards the data slot 501 of the output TDM cell to the BBU 201 in thecentral controller G. At block 604, the UL-TDM switch forwards data bitsin a second slot of the first plurality of TDM data slots in the secondTDM cell to an uplink TDM switch in a different IC. For example, theUL-TDM switch 202 places data bits in the data slot 502 of the input TDMcell in the data slot 502 of the output TDM cell and forwards the dataslot 502 of the output TDM cell to the UL-TDM switch 302 in the centralcontroller I through the Ethernet link 331.

FIG. 7 shows a flowchart chart of a method 700 for switching a downlinkchannel stream, according to one embodiment herein. At block 701, aDL-TDM switch generates a third TDM cell based on digital signalsreceived from the BBU coupled to the DL-TDM switch in the IC, whereinthe third TDM cell comprises a third plurality of TDM data slots. Forexample, as described above, the DL-TDM switch 324 generates a third TDMcell 500 based on the received baseband digital signals from the BBU321. The third TDM cell 500 includes data slot 501 and data slot 502. Atblock 702, for each TDM data slot in the third TDM cell, the DL-TDMswitch forwards data bits in the TDM data slot to either the first RH orto a DL-TDM switch in a different IC. For example, the DL-TDM switch 324forwards data bits in the data slot 501 to the RH physically connectedto the central controller C. Also, the DL-TDM switch 324 forwards databits in the data slot 502 to the DL-TDM switch 314 through the Ethernetlink 340.

In one embodiment, TDM cells are transmitted over Ethernet links withdifferent directions or destinations. In one embodiment, all the dataslots in the TDM cells are either received on an Ingress port or sent onan Egress port. In one embodiment, all the data slots in the TDM cellseither come directly from the sender as the original data source or passthrough the sender which acts as a relay for the original data source.In one embodiment, all the data slots in the TDM cells are eithertransmitted directly to the receiver as the final destination or passthrough the receiver which acts as a relay for the final destination. Inone embodiment, the TDM switch (either the UL-TDM switch or the DL-TDMswitch) receives data slots from Ingress TDM cells and places thereceived data slots in data slots of the Egress TDM cells.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

In the preceding, reference is made to embodiments presented in thisdisclosure. However, the scope of the present disclosure is not limitedto specific described embodiments. Instead, any combination of thedescribed features and elements, whether related to differentembodiments or not, is contemplated to implement and practicecontemplated embodiments. Furthermore, although embodiments disclosedherein may achieve advantages over other possible solutions or over theprior art, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the scope of the present disclosure. Thus,the preceding aspects, features, embodiments and advantages are merelyillustrative and are not considered elements or limitations of theappended claims except where explicitly recited in a claim(s).

Aspects of the present invention may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.”

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic link), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission links, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

We claim:
 1. A system, comprising: a plurality of radio heads, whereineach of the plurality of radio heads comprises at least one antenna andat least one transceiver; a plurality of controllers disposed in one ormore chassis external to the plurality of radio heads, wherein each ofthe plurality of controllers comprises: a baseband unit (BBU); an uplinktime-division multiplexing (TDM) switch coupled to (i) at least a firstradio head of the plurality of radio heads, (ii) the BBU in thecontroller, and (iii) at least one uplink TDM switch in a firstdifferent controller of the plurality of controllers, and wherein theuplink TDM switch is configured to: receive a first TDM cell based onsignals received from the first radio head, wherein the first TDM cellcomprises a first plurality of TDM data slots, and wherein a destinationof each of the first plurality of TDM data slots is predetermined;generate a second TDM cell based on the first TDM cell, wherein thesecond TDM cell comprises a second plurality of TDM data slots, andwherein a destination of each of the second plurality of TDM data slotsis predetermined; forward data bits in a first slot of the firstplurality of TDM data slots to the BBU in the controller; and forwarddata bits in a second slot of the first plurality of TDM data slots inthe second TDM cell to the at least one uplink TDM switch in the firstdifferent controller; and a downlink TDM switch coupled to (i) the firstradio head, (ii) the BBU in the controller, and (iii) at least onedownlink TDM switch in a second different controller of the plurality ofcontrollers, and wherein the downlink TDM switch is configured to:generate a third TDM cell based on digital signals received from the BBUin the controller, wherein the third TDM cell comprises a thirdplurality of TDM data slots; and for each TDM data slot in the third TDMcell, forward data bits in the TDM data slot to either the first radiohead or to the at least one downlink TDM switch in the second differentcontroller.
 2. The system of claim 1, wherein the uplink TDM switch isconfigured to forward data bits in the second slot of the firstplurality of TDM data slots to the at least one uplink TDM switch in thefirst different controller through an I/O interface.
 3. The system ofclaim 1, wherein the uplink TDM switch and the downlink TDM switch arecoupled to the first radio head through a same I/O interface.
 4. Thesystem of claim 1, wherein the uplink TDM switch and the downlink TDMswitch are the same switch.
 5. The system of claim 1, wherein thedestination of each of the first plurality of TDM data slots ispredetermined based on bit positions of the data slots in the first TDMcell.
 6. The system of claim 1, wherein each of the plurality ofcontrollers is configured to provide part or all of a digital part of aphysical (PHY) layer function and a media access control (MAC) layerfunction of an access point (AP) without providing a analog part of thePHY layer function of the AP.
 7. An integrated circuit, comprising: abaseband unit (BBU); an uplink time-division multiplexing (TDM) switchcoupled to (i) at least a first radio head, (ii) the BBU in theintegrated circuit, and (iii) at least one uplink TDM switch in a firstdifferent integrated circuit, and wherein the uplink TDM switch isconfigured to: receive a first TDM cell based on signals received fromthe first radio head, wherein the first TDM cell comprises a firstplurality of TDM data slots, and wherein a destination of each of thefirst plurality of TDM data slots is predetermined; generate a secondTDM cell based on the first TDM cell, wherein the second TDM cellcomprises a second plurality of TDM data slots, and wherein adestination of each of the second plurality of TDM data slots ispredetermined; forward data bits in a first slot of the first pluralityof TDM data slots to the BBU in the integrated circuit; and forward databits in a second slot of the first plurality of TDM data slots in thesecond TDM cell to the at least one uplink TDM switch in the firstdifferent integrated circuit; and a downlink TDM switch coupled to (i)the first radio head, (ii) the BBU in the integrated circuit, and (iii)at least one downlink TDM switch in a second different integratedcircuit, and wherein the downlink TDM switch is configured to: generatea third TDM cell based on digital signals received from the BBU in theintegrated circuit, wherein the third TDM cell comprises a thirdplurality of TDM data slots; and for each TDM data slot in the third TDMcell, forward data bits in the TDM data slot to either the first radiohead or to the at least one downlink TDM switch in the second differentintegrated circuit.
 8. The integrated circuit of claim 7, wherein theuplink TDM switch is configured to forward data bits in the second slotof the first plurality of TDM data slots to the at least one uplink TDMswitch in the first different integrated circuit through an I/Ointerface.
 9. The integrated circuit of claim 7, wherein the uplink TDMswitch and the downlink TDM switch are coupled to the first radio headthrough a same I/O interface.
 10. The integrated circuit of claim 7,wherein the uplink TDM switch and the downlink TDM switch are the sameswitch.
 11. The integrated circuit of claim 7, wherein the destinationof each of the first plurality of TDM data slots is predetermined basedon bit positions of the data slots in the first TDM cell.
 12. Theintegrated circuit of claim 7, wherein the integrated circuit isconfigured to provide part or all of a digital part of a physical (PHY)layer function and a media access control (MAC) layer function of anaccess point (AP) without providing a analog part of the PHY layerfunction of the AP.
 13. A controller, comprising: a baseband unit (BBU);a memory containing a program that, when executed on the BBU, performsan operation, the operation comprising: receiving a first TDM cell basedon signals received from a first radio head, wherein the first TDM cellcomprises a first plurality of TDM data slots, and wherein a destinationof each of the first plurality of TDM data slots is predetermined;generating a second TDM cell based on the first TDM cell, wherein thesecond TDM cell comprises a second plurality of TDM data slots, andwherein a destination of each of the second plurality of TDM data slotsis predetermined; forwarding data bits in a first slot of the firstplurality of TDM data slots to the BBU in the controller; forwardingdata bits in a second slot of the first plurality of TDM data slots inthe second TDM cell to at least a first different controller; generatinga third TDM cell based on digital signals received from the BBU in thecontroller, wherein the third TDM cell comprises a third plurality ofTDM data slots; and for each TDM data slot in the third TDM cell,forwarding data bits in the TDM data slot to either the first radio heador to at least a second different controller.
 14. The controller ofclaim 13, wherein forwarding data bits in the second slot of the firstplurality of TDM data slots to the first different controller comprisesforwarding data bits in the second slot of the first plurality of TDMdata slots to the first different controller through an I/O interface.15. The controller of claim 13, wherein the destination of each of thefirst plurality of TDM data slots is predetermined based on bitpositions of the data slots in the first TDM cell.
 16. The controller ofclaim 13, wherein the controller is configured to provide part or all ofa digital part of a physical (PHY) layer function and a media accesscontrol (MAC) layer function of an access point (AP) without providing aanalog part of the PHY layer function of the AP.
 17. The controller ofclaim 13, wherein the controller is disposed in a chassis external tothe first radio head.